Electronic components such as semiconductor devices installed in electric/electronic devices produce an increased amount of heat due to high density packaging or the like along with improvement in functionality, and importance of cooling of such electronic components is increasing recently. Planar heat pipes may be used for cooling electronic components.
When a copper material, which is a material having excellent compatibility with water, which is a widely-used working fluid, is used as a container material of a planar heat pipe, in order to seal a hollow portion having a wick structure, it is common to join a periphery of the hollow portion by brazing or soldering, since a copper material has a high thermal conductivity and a low electric resistance. However, with a sealing method using brazing or soldering, it is necessary to heat copper material, which is a container material, at a high temperature, and thus there is a problem of a tendency that a rigidity of the container material decreases and a pressure resistance of the planar heat pipe deteriorates.
On the other hand, when a material other than a copper material, e.g., stainless steel, is used as a container material to prevent the decrease in pressure resistance of the planar heat pipe due to brazing or soldering, there is a problem of a poor compatibility with water, which is a widely-used working fluid.
Further, a cladded material including two types of metal members may be used as a container material. A planar heat pipe has been proposed in which a member having a double-layered structure of a copper material and an aluminum material is used as a cladded material to reduce weight and improved workability, and a surface of the cladded material forming the wall of the container is made of a copper material (Patent Document 1).
However, the planar heat pipe of patent document 1 includes a copper material and an aluminum material, which are both materials having a relatively high thermal conductivity, and thus the container may deform upon sealing the hollow portion described above by laser beam welding or by resistance welding.